1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device including a transistor.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a storage device, a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
Various metal oxides are used for a variety of applications. For example, indium oxide, which is a well-known metal oxide, is used as a transparent electrode material in liquid crystal display devices and the like.
Some metal oxides have semiconductor characteristics. Metal oxides having semiconductor characteristics are a kind of compound semiconductor. The compound semiconductor is a semiconductor formed by two or more kinds of atoms bonded together. In general, metal oxides serve as insulators; however, it is known that metal oxides serve as semiconductors depending on the combination of elements included in the metal oxides. For example, it is known that tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like have semiconductor characteristics. A technique is disclosed in which a transistor manufactured using zinc oxide or an In—Ga—Zn-based oxide is used as a switching element or the like of a pixel of an active matrix display device (see Patent Documents 1 and 2).
Transistors including oxide semiconductors have higher field-effect mobility than transistors including amorphous silicon. Therefore, driver circuits of display devices and the like can be formed using the transistors including oxide semiconductors.
Display devices include electroluminescent (EL) display devices, electronic paper, and liquid crystal display devices. Among these, active matrix EL display devices capable of displaying high-resolution images are particularly attracting attention. In an active matrix EL display device, where a plurality of switching elements are arranged in pixels, voltage is applied to a light-emitting element electrically connected to at least one of the switching elements, whereby electrons and holes are separately injected from a pair of electrodes into a layer containing a light-emitting organic compound, and current flows. The carriers (electrons and holes) are recombined, and thus, the light-emitting organic compound is excited. The light-emitting organic compound returns to a ground state from the excited state, thereby emitting light. Owing to such a mechanism, this light-emitting element is referred to as a current-excitation light-emitting element.
The range of uses of an active matrix display device is expanding, and demands for larger screen size, higher definition, and higher aperture ratio are increasing. In addition, it is demanded that a production method of the active matrix display device offer high productivity and reduced production cost.